A characteristic of continuous casting installations is a mold having opposite open ends. Molten material is introduced into one of the ends of the mold and partially solidifies therein to form a solidified shell with a molten core. The shell issues from the other end of the mold in the form of a continuous strand.
A strand must be started at the beginning of the casting operation and a dummy or starter bar is used for this purpose. This bar has a head which conforms to the cross-section of the mold cavity and fits therein with close clearance. The dummy bar head is inserted in the mold cavity prior to starting the cast and the spaces between the dummy bar head and the inner walls of the mold are then usually sealed. Thereafter, molten material is admitted into the mold cavity. The first quantities of molten material admitted into the mold cavity solidify in contact with the dummy bar head. Once this has occurred, the dummy bar head is withdrawn from the mold in any suitable manner. The dummy bar head draws the cast strand behind it until the strand can be engaged by the driven rollers of the casting installation. The dummy bar head and the strand are then disconnected. The rate of withdrawal of the dummy bar head from the mold, as well as the rate of withdrawal of the strand by the driven rollers of the casting installation once the strand has been disconnected from the dummy bar head, are so related to the rate of introduction of molten material into the mold that a solidified shell with a molten core always issues from the mold.
The dummy bar head is provided with some form of coupling means so that a connection may be formed between the strand and the dummy bar head.
One known type of dummy bar head has no coupling means of its own. A coupling element, e.g., a bolt, is secured to the dummy bar head before the start of a cast. This coupling element is disconnected from the dummy bar head after the strand has been started. It is generally intimately connected with the leading crop end of the strand and is discarded therewith. As a result, it becomes relatively expensive to operate with this type of dummy bar head when large numbers of multiple strand casts must be started.
This problem is alleviated by using a dummy bar head having coupling means permanently associated therewith. The present invention is mainly concerned with a dummy bar head of this type and with a method of connecting such a dummy bar head with the cast strand.
A known dummy bar head with permanent coupling means is provided with a notch which forms a hooklike cavity in conjunction with the adjacent wall of the mold. Molten metal flows into the hooklike cavity. Upon solidification of the molten metal, a connection in the form of interlocking hooks is formed between the dummy bar head and the solidified molten metal. The connection may be broken by moving the dummy bar head sideways relative to the strand. This dummy bar head works well for the casting of slabs where the latter are guided and supported by closely spaced pairs of rollers between the mold and the location where the dummy bar head is disconnected from the strand. In this case, the close confinement of the dummy bar head and the strand prevents premature disconnection thereof. However, where the dummy bar head and the strand are not closely confined, as is usually the case in the casting of strands such as blooms and billets which are of smaller cross-section, the dummy bar head tends to disconnect from the strand prematurely. This is particularly true where the dummy bar head and the strand move along a curved path. Other disadvantages associated with this dummy bar head are as follows: it is difficult to seal in the mold since certain of the edges which must be sealed are not readily accessible; and it is difficult to machine and recondition due to the configuration of the notch provided therein.
In a modified form of the above dummy bar head, the notch is undercut. Although this alleviates the tendency of the dummy bar head to disconnect from the strand prematurely, the undercut configuration gives rise to another difficulty. Thus, the dummy bar head does not disconnect from the strand in a smooth and trouble-free manner.
A dummy bar head bearing a similarity to that discussed above also forms a connection with the strand via interlocking portions on the strand and the dummy bar head. Here, the configuration is such that, as opposed to the previously-described dummy bar head, the connection between the strand and the dummy bar head is broken by rotating the latter relative to the strand. This dummy bar head suffers the same disadvantages as the one discussed above.
Other dummy bar heads having permanent coupling means are known. However, all of these exhibit the common disadvantage of being difficult to seal in the mold.